Inflatable core



Aug. 3, 1954 E. T. HUNTER 2,685,118

INFLATABLE CORE Filed Aug. 9, 1950 FIQI. 2

2 Sheets-Sheet l F|c.3. T3 7 F|c.4.

INVENTOR ELOREDT. HUNTER ATTOR NE YJ E. T. HUNTER INFLATABLE CORE Aug.3, 1954 2 Sheets-Sheet 2 Filed Aug. 9, 1950 INVENTOR I. THILZZZZATTORNEYS.

Patented Aug. 3, 1954 UNITED STATES FATENT OFFICE 2,685,118 INFLATABLECORE Eldred Tait Hunter, Washington, D. 0. Application August 9, 1950,Serial No. 178,536 Claims priority, application Great Britain August 16,

3 Claims.

The present invention relates to an inflatable core.

from the set mass.

It is a further object to provide an inflatable It is an additionalobject to provide an inflatable rubber core made in long lengths andrelative small diameters, these diameters generally not exceeding fourinches after inflation.

While inflatable cores per se are known, the prior art devices cannot beproduced in long lengths and small diameters.

The accompanying drawing shows several examples embodying the featuresof the present invention wherein:

Figure 1 is a longitudinal view of the mandrel used in making the rubbercore with the original layer of rubber applied thereto,

Figure 2 is a cross section of Figure 1 taken on line 22 of Figure 1,

Figure 3 is a longitudinal view of the mandrel with the inner rubbershown in Figure 1 and the core braid applied thereto,

Figure 4 is a cross sectional view taken on line 44 of Figure 3,

Figure 5 is a longitudinal view of the mandrel, the original rubber, thebraid and the outer rubber coating applied thereto,

Figure 6 is a sectional view taken on the line 6-6 of Figure 5,

Figure 7 is a longitudinal view of the finished core showing the angleof application of the outer layer of rubber,

Figure 8 is a diagrammatic view partly broken away to disclose thevarious expansible and contractable cord sheath 3 illustrated in Figures3 to 6 and 8. The cords of this sheath are made up of a number of cottonstrands having minimum stretch characteristics, a low moisture contentand which strands are twisted together.

are closely laid on to the rubber layer so as to The resulting inbersheath 4, as shown in Figures 5 and 6. This outer rubber sheath is ofgreater thickness than the initial rubber layer 2 and the rubberutilized in this layer has the same characteristic as to purity as thefirst-mentioned layer. Preferably the outer rubber sheath is applied asa continuous strip spiral wound, as shown in Figure '7. The strip isapplied in an uncured or tacky state. The outer rubber sheath can beapplied as an envelope, that is, a strip having such width that it canenvelope the mandrel, the layer 2 and the sheath and have the end edgesabut to provide what amounts to a longitudinal seam running throughoutthe length of the core. After the outer sheath of rubber is applied acanvas wrapping or wrappings is applied over the previously mentionedlayers. This canvas wrapping can constitute one or more layers in theform of an envelope and an outer layer that is spirally wound thereaboutunder tension. By applying this outer canvas layer in a spiral woundmanner or when only a spiral wound layer of canvas wrapping is utilizedthe application of tension in the winding of the wrapping at an angle tothe axis of the core imparts a twist characteristic to the rubber layerand which twist characteristic remains when the rubber is cured. Afterthe canvas wrapping has been applied as indicated in Figure 8, the corelength is substantially iinmediately placed in a suitable oven and heattreated to cure or set the rubber layers. This is a conventional curingoperation except as to the time element between wrapping and curing andone generally utilizing steam. After the core has been cured the canvaswrapping is removed and the mandrel is removed, preferably with the aidof air pressure.

The foregoing steps have produced a fifty foot length of tubing havingcharacteristics described hereinafter. This tubing can produce a core offifty foot lengths or the tubing can be cut to provide cores of shorterlengths or connected together to provide cores of longer lengths. Tocomplete the manufacture of a core a suitable solidplug or closure 1 isinserted in 2 the desired length of tubing and metal rings or clamps 8are tightly applied to the outside of this solid plug in position. Thejoint must be sufficiently tight to retain the plug in place under theaction of air pressure up to 150 pounds per square inch. The other endof the core length receives in a similar manner a tubular plug H3provided externally with a conventional Schrader tire valve. As shown inFigure 9 rings or clamps H are tightly applied to the outer sheath 4 tosecure the tubular plug is in position. We therefore have an inflatablecore of the desired length and it is further noted that the solid plug 1protrudes from the end of the core a length sufficient to receive atransverse bore 9 and which bore is utilized to receive a fish line orleader so that as the core is removed an electrical wire or otherconduit can be connected to the plug and drawn into the tube or ductproduced utilizing the inflatable core.

The braid is applied directly on the inner rubber layer 2 while the sameis still wet or tacky and in order to enable an even expansion of thefinished core upon inflation it is desirable that the angle between eachstrand of braid and a line on the surface of and parallel to the axis ofthe core when inflated should preferably be be tween 42 and 53. In orderto obtain such an angle of the braid it has been found desirable toapply the braid onto the inner rubber 2 so that it makes an angle ofbetween 13 and 19 with the axis of the unexpanded core in the case ofmandrel diameters between and $5 and from 17 to 25 for larger mandreldiameters of the order of 1 A".

The inner rubber and braid will tend to free itself from the surroundingrubber of the outer sheath 4 and hence during inflation of the fin--ished core the braid will limit the expansion and provide an evenexpansion over the length of the core, the braid changing its angle fromthat at which it was braided e. g. about 13l9 to an angle of 42 to 53when the core is expanded.

When the fluid in the core is brought under pressure, less than lbs. persquare inch, usual- J ly in the neighborhood of 40 to '70 lbs. persquare will shorten in length and increase This is then surrounded bywet concrete and on deflation after the concrete has hardened'the corewill increase in length and decrease in diameter and will come free ofthe concrete allowing the core to be removed to leave the desired duct.The change in angle of the braid during deflation of the core will causethe latter to contract and lengthen during deflation thus assisting infreeing it from the surrounding concrete.

The outer coating is applied over the treated cord in a continuous stripwound spirally thereon. This is held in place during the first heattreatment and the subsequent steam curing by means of canvas wrappingapplied to the surface thereof, so as to obtain a uniform product of thedesired outside diameter.

The core made by the inch, the core in diameter.

above process will have an inner wall thickness varying from inch toinch depending on the outside diameter of the finished core. The abovethicknesses are given for a finished core of inch to 2 inches, which maybe inflated to 1 inch to 4 inches.

One size ismade on a mandrel of an inch in diameter upon which isapplied the inner rubber layer of an inch thick. On this is braided thecord treated withrubber cement and then an external layer of rubber isapplied thereon which is approximately of an inch thick. The outsidediameter of the finished core is 1% inch and may be expanded toapproximately 2 inches, using an internal fluid pressure of 40 to '70lbs. This will vary depending upon the age of the product, the heavierpressure being necessary with newly made cores. The core is loosenedwithin its surrounding rubber to give a free working restricting sheathsurrounding the inner rubber tubing. 7

This process of using a long mandrel up to 50 feet on which is coated apure rubber layer and then braiding directly on to the uncured rubber acord sheath, treating the cord sheath with a rubber cement and applyingto this the outer layer of rubber in a tacky condition has led to theproduction of a satisfactory product where many others have failed.Cores of this type may be made with any outside diameter, which ininflation will range from 1 inch to four inches.

These cores are strong, will stand the rough treatment to which they aresubjected, are air tight, may be readily inflated by either a hand pumpor compressed air tank and upon deflation will not cling to the cementwalls of the conduit formed, and will increase in length so as to bereadily removed from the finished conduit.

In connection with the finished core the spiralwinding of the canvaswrapping 5 is such that tension is applied to the wrapping as it isbeing wound on the outer layer 4 and this tension as indicatedpreviously imparts a twist charactersary to inflate each lengthseparately but the istic to the rubber even though it is unset andincreased length of tubing is still highly desirable upon subsequentcuring this twist is retained in some installations.

in the rubber. This twist characteristic is im- With this type jointupon inflation of the two will twist to restore itself to its originalcondithls JO n can only be broken by defla i t tion and this twistaction in deflating will deflsp ct ve Co snitely improve the ease ofremoval of the core -If larger ducts are required in concrete they fromthe surrounding concrete or other plastic can be obtained from a singlecore the increased mass. In other words, every particle of rubberdiameter can be Obtained by tying u s Cores of the outer sheath hasmoved when the core is together a d us them as a it- F p deflated and ineffect physically tears itself away a duct appreXimately by in e n bfrom any adherence to the inner surface of the Obtained y using sixexpanded d. COI'eS duct or tube made in the concrete or like matetiedtogether as a ni y tyi g t t I The canvas wrapping is approximately 3"Wide for example, the use of rubber bands holding and the twist isimparted t th rubber by 13- 2 them in assembled relationship.Alternatively plying greater tension to one marginal edge of severalcores can be inflated, placed in parallelthe wrapping as it is beingapplied. I th ism and tied together by wire, then placed in ber undergreater tension than the other side 25 diameter and an be individuallyWithdrawn and of the strip, see Figure 8. Thus in a finished the wire yembodied in the concretetube or core slight spiral ridges are formed inIt is further noted at While the m nd the outer surface of the outersheath and alterlength is stated to be approximate y 5 f long, nateedges of the ridges are mor pronounced, ther is of course no limitationto the length of In connection with the braiding of the fabric themandrel Other than e l th f the 000kcore or sheath on to the innerrubber layer by e Oven ed to Cure t e rubber; for examp applyingslightly greater t n io t s of in European practice the ovens areapproxithe cords being braided from one side of the mately 0 feet longthus necessitating the use of axis of the tube and by braiding uniformlya a 0 foot m d n a y g ut th pr stwisting movement is produced over thwhole f lar er ovens a e ava lable, he mand l ca length of the tubewhich enhances the twist be l n h n ac or in lycharacteristic applied tothe finished core as t I C m shown in Figure 8. 1. An inflatable conduitcore comprising a comt is to be noted that the spiral wrapping 5 positetube including an inner rubber layer, a is applied at an an le i th sdirection as 40 braided cord sheath applied thereto with the the braidtension. Thus it follows that the braidcords f h h h being i n l and t nin imparts a twist to the inner rubber layer angle of between 13 and 25/2 W th respect to which constitutes an expansible and contractable theaxis of the tube and some of the diagonal tube which twist is assistedby the twist imparted cords of the braided sheath on one side of thecontraotable tub by the tensionjng of th canvas tension than the othercords, and an outer rubber wr p in 5, sheath tensioned in the samedirection as said Thus it follows that when using my inflatable rd sh ata plug l sin on end f th tu cores and they are inflated to the sizerequired and. a, valve disposed at the other end of said utilizing 59 to70 lbs. pressure and substantially [)0 tube so that the core can beinflated and upon oil free air, the diameter of the tube increasesinflation t e u e Wi l s rt n a d the cords of uniformly as it isinflated and the braided sheath t sh th w l tra t to a su an angle ofcontracts lengthwise so that the length of the between 42 and 53relative to the axis of the tube decreases uniformly by about 15 er centtube whereby the expansion of the tube is reand since, as previouslymentioned, one or more 55 ra n d u f m Da SiO by th tens o in cords ofone set of the diagonal cords of the 0f the cords 0f the sheath and therubber of fabric sheath is braided with a slightly greater the u r S eattension, there is produced a twisting movement 2. An inflatable conduitcore comprising a over the whole length of the tube. The tensioncomposite tube including an inner rubber layer, applied to the cords isof the order of a few a braided cord reinforcing sheath appliedthereounces, preferably one to three ounces, greater to with the cordsthereof being diagonal and than the tension in the other cords, Thisaction some of the diagonal cords on one side of the therefore impartsthree distinct movements longitudinal axis of the core being undergreater w i breaks any y 01 s etw en con rete tension than the othercords, and an outer ruband the tube in use when the tube is deflated. eber sheath encompassing said braided sheath st, t e decrease indiameter; second, the inand tensioned in the same direction as thecrease in length, and finally, the twist of the greater tensioned cords.core. 3. An inflatable conduit core comprising a com- As previouslyindicated longer runs of inflatposite tube including an inner rubberlayer, a able core can be produced by joining two lengths braided cordreinforcing sheath applied thereto to h r. u h a J int m die a plac n fwith the cords thereof being diagonal and some the plug ends in abuttingrelation and a sleeve of the diagonal cords on one side of the longi-01' l n th of tubing 0f th quired duct internal tudinal axis of the corebeing under greater diameter is deposited about the abutting ends.tension than the other cords, an outer rubber Of course, in such anarrangement it s n ssheath encompassing said braided sheath andtensioned in the same direction .as the tensioned Number Name Datecords, means closing one end of the composite 1,214,268 Blodgett Jan.30, 1917 tube, and valved means closing the other end 1,230,867 CobbJune 26,1917 of the tube and operative to permit inflation of 1,352,740Egerton Sept. 14, 1920 thecore. 5 1,428,201 Andrews Sept. 5, 19221,981,201 Semler Nov. 20, 1934 References Cited in the file of thispatent 2,035, 0 Lippitt Man 3 93 UNITED STATES PATENTS 3,090,014 115 A 11 7 392,992 at in Jan. 15, 1946 Numbel Name Date 10 2,482,702 BillmeyerSept. 20, 1949 1,190,292 Hopkins July 11, 1916

